Calreticulin expression in relation to exchangeable Ca2+ level that changes dynamically during anthesis, progamic phase, and double fertilization in Petunia

• Published in: Planta 2015-01, Vol.241 (1), p.209-227
• Main Authors: Lenartowski, Robert, Suwińska, Anna, Lenartowska, Marta
• Format: Article
• Language: English
• Subjects: Agriculture; Biomedical and Life Sciences; calcium; calreticulin; Ecology; embryogenesis; endoplasmic reticulum; flowering; Forestry; gametophytes; genes; Life Sciences; Original; Original Article; ovules; Petunia hybrida; pistil; Plant Sciences; pollen; pollen germination; pollination; sexual reproduction; spermatozoa; sporophytes; stigma
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-014-2178-z

Calcium (Ca²⁺) plays essential roles in plant sexual reproduction, but the sites and the mechanism of Ca²⁺mobile storage during pollen–pistil interactions have not been fully defined. Because the Ca²⁺-buffering protein calreticulin (CRT) is able to bind and sequester Ca²⁺, it can serve as a mobile intracellular store of easily releasable Ca²⁺and control its local concentration within the cytoplasm. Our previous studies showed an enhanced expression of Petunia hybrida CRT gene (PhCRT) during pistil transmitting tract maturation, pollen germination and tube outgrowth on the stigma, gamete fusion, and early embryogenesis. Here, we demonstrate that elevated expression of CRT results in the accumulation of this protein in response to anthesis, pollination, sperm cells deposition within the receptive synergid and fertilization, when the level of exchangeable Ca²⁺changes dynamically. CRT localizes mainly to the endoplasmic reticulum and Golgi compartments in the pistil transmitting tract cells, germinated pollen/tubes, and sporophytic/gametophytic cells of the ovule and corresponds with loosely bound Ca²⁺. Additionally, the immunogold research shows, for the first time, highly selective CRT distribution in specific nuclear sub-domains. On the basis of our results, we discuss the possible functions of CRT with respect to the critical role of Ca²⁺homeostasis during key events of the multi-step process of generative reproduction in angiosperms.